Todd Akin, the embattled Republican Senate candidate whose remarks on "legitimate rape" prompted calls for him to exit the Missouri race, is now 10 points behind his rival, according to a Rasmussen poll released on Thursday.

The poll, which also found 63% of voters now view him unfavourably, is a major blow to the candidate who has haemorrhaged support from his party since his remarks on Sunday. Only last week, he was leading by nine points, according to one poll.

Carried out on Wednesday, three days after his comments on abortion and rape, the new poll shows Claire McCaskill, the Democratic incumbent, with 48% and Akin with 38%. The new figures show a big swing from the previous Rasmussen poll in July in which he came out three points ahead.

Of those who responded to the poll, 47% said they now have a very unfavourable view of Akin, while 16% said they had a somewhat unfavourable view of him. However, when asked if Akin should drop out of the race, 42% said no and 41% said yes.

The Missouri seat is an important one for Republicans, because it was seen as one of the most winnable for them. The Republicans, already in control of the House, are four seats away from taking control of the Senate.

In a further setback for Akin, he has raised just $100,000 in an online fundraising drive that he called a message to "party bosses" about his commitment to the Missouri Senate race.

That is well below the amount he needs to keep his campaign afloat after he lost the funding of major backers, including $5m from the conservative Super Pac Crossroads GPS. The National Republican Senatorial Campaign also pulled funding.

Akin posted on Twitter that thousands of donors had come forward to help him surpass the fundraising target he sought to achieve by the end of Wednesday.

His jubilant Twitter message that "voters should pick candidates not party bosses" came before the latest poll results.

Thousands of people stepped up and helped us raise over $100,000! The message is clear... voters should pick candidates, not party bosses.

Akin's claim that pregnancies from "legitimate rape" are rare because "the female body has ways to try to shut that whole thing down", caused widespread outrage. Republican leaders, including Mitt Romney and Paul Ryan, who contacted him personally, publicly called on him to step aside.